System of radiocommunication



Au 5, 1930. H F RB 1,772,077

SYSTEM OF RADIO COMMUNICATION Filed Sept. 16, 1926 Patented Aug. 5, 1930 UNITED. STATES PATENT OrFicE HENRY o. FORBES, OF CHICAGO, ILLINOIS, AssIenoR T0 ZENITH RADIO CORPORATION,

or CHICAGO, ILLINOIS, A ooaronsrron or ILLINOIS SYSTEM OF RADIOCOMMUNIGATION Application filed September 16', 1926. Serial No. 135,826.

My invention relates to systems of radio communication and is of particular use in those systems wherein the sending and receiving stations are not liar apart.

The system of my invention is especially useful when employed in establishing communication between stations upon locomotives and the cars of a train. The invention is of much service in establishing communication between attendants upon the locomotives and cabooses of freight trains.

While the invention thus finds especial utility, it is not to be limited to any particular use.

It is the object of my invention to include signaling apparatus in the system whereby an operator or attendant at either station may signal an operator or attendant at the other station. Generally. speaking, the radio system of communication of my invention employs an antenna, a circuit having means therein for generating and impressing upon said antenna a wave form carrier current, a telephonic circuit including a telephonic transmitter, a signaling circuit, a modulating thermionic valve interposed between said wave form carrier current circuit and said telephonic and signaling circuits, and means included in the signaling circuit serving as a generator of signaling current. In the preferred embodiment of the invention, the means for generating the wave form carrier current and the means for generating the signaling current are in the form of thermionic valves.

The signaling apparatus desirably furnishes audible signals, a result which is preferably secured by a modulation of the carrier current wave by a signaling current wave of approximately 800 cycles, the modulations thus impressed upon the carrier current wave at the sending station causing an audible signal at the receiving station and preferably in a loud speaker located at the latter station. Such a signal, in railroad practice, is easily discernible through the rumbling noises made by the moving train and the higher pitched noises such as those caused by steam whistles.

I will explain my invention more fully by reference to the accompanying drawing which diagrammatically illustrates the pre ferred embodiment thereof.

In the system illustrated, the antenna 1. is grounded through a winding 2. A winding 3, in conjunction with the winding 2 to which it is inductively related couples the antenna with a circuit in which a wave form carrier current is generated and upon which'signaling-and telephonic current modulations are adapted to be impressed. This circuit is illustrated as being inclusive of an Oscillator in tie form of a thermionic valve 4 employing a grid 5, a plate 6, and a filament or cathode 7. The grid is connected with one terminal of the winding 3 by way of the condenser 8. The other terminal of the winding 3 is connected with the plate 6 through the condenser The filament 7 is supplied with current from a battery 10. A source of direct current .11 is connected between the filament 7 and the plate 6 by way of the air core choke coil 12. The conductor 13 by which one pole of the generator 11 and one pole of the battery 10 are connected with the filament 7 is desirably adjustably connected with the winding 3. The antenna l-is thus coupled with a circuit in which wave form carrier current is generated.

A local telephonic circuit includes a telephonic transmitter 14, the primary winding 15 of an inductive coupler 15-18, a battery l6,and a circuit opening and closing switch arm 17. The secondary 18 of coupler 15-18 has one terminal connected with the grid 19 of a thermionic valve 20, this valve having a plate 21 connected with the conductor 13 and a filament .or cathode 22 supplied with current from a battery 23. lVhen the switch 17 is closed and the transmitter lispoken into, telephonic current changes are impressed upon the wave form carrier current circuit by way of the thermionic valve 20 which serves to modulate the wave form carrier current-under the control of the telephonic circuit- The circuit that includes the grid 19 and the telephonic secondary 18 also includes a signaling secondary 24; whose complemental primary 25 is included in an inducing signaling circuit which also contains aplate 26 of a thermionic valve 27, and the adjustable switch arm 28. The grid 29 of the valve means operable at will to close said telephonic 27 is connected with the circuit of grid 19 circuit and open the output circuit of said between the windings 18 and 24:. The filasecond valve, and vice versa. ment or cathode 30 is supplied with current In witness whereof, I hereunto subscribe from the battery 23. The switch arms 17 and my name. 70

28 are coupled by the switch lever 31 so that 1 HENRY C. FORBES. when either switch closes the circuit to which 1 i it pertains, the other switch opens the circuit to which it pertains. The Valve 27 serves to generate wave form signaling currentof,say, i e l i 75 800 cycles. The current oscillations thus gen-' I erated are applied to the grid-filament circuit of valve which includes the windings 18 and 24. The valve 20 is common to the 15 signaling and telephonic circuits and serves 80 to modulate the carrier current circuit under the control of either of these circuits according to the adjustment of the switch lever'31.

Changes may be made without departing V v 2 from the invention. r e 85 Having thus described my invention, I claim; I

1. In a radio system of communication, the combination, with an antenna and a circuit having a first thermionic valve therein op- 90 crating to generate and impress upon said antenna a wave form carrier current, of a telephonic circuit including a telephonic transmitter; a signaling circuit having a second thermionic valve thereinv operating to generr ,95

ate wave form signaling current; a coupling circuit having a third thermionic valve therein, the output of which is connected with the input circuit of said first valve and the input v circuit of which is connected with the input 100 circuit of said second valve; a plurality of transformers, the secondary windings of which are included in the input circuit of said third valve, and the primary windin 's of 40 which are included, one in the said telep onic 105 circuit and the other in the said signaling circuit; and means operable at will to selectively open one and close the other of said telephonic and signaling circuits.

2. In a radio system of communication,

the combination with an antenna and a circuit having a first thermionic valve therein operating to generate and impress upon said antenna a wave form carrier current, of

a telephonic circuit including a telephonic transmitter and a first transformer primary winding; a signaling circuit having a second theremionic valve therein operating to generate a signalling current and having a second transformer primary winding in the output circuit of said second valve; a third thermionic valve operating as a modulator under the control of said telephonic circuit, the output of said third valve being connected with the input of said first valve and the input of said third valve being connected with the input of said second valve and having first and second transformer secondary windings complemental respectively to said first and second transformer primary windings; and 

